Diver propulsion vehicles are used to propel scuba divers underwater during underwater expeditions. One performance factor that can be important to the user is the run time/range of the vehicle. Longer run times/ranges are desirable. Two other factors of importance to the usability and availability of the vehicle are its size/weight and cost. Large size, weight, and cost are detrimental.
A battery is typically used to power such a vehicle. The battery is conventionally a large component in the vehicle, so this increases the size and weight and/or increases the cost. However, there are other aspects of the vehicle that effect performance in terms of range and run time.
In conventional diver propulsion vehicles, the speed or thrust of the vehicle is regulated by adjusting the pitch of the propeller. However, such propellers are not optimized for efficiency and are susceptible to propeller deflection at high speeds, leading to further losses in efficiency. Low efficiencies means more battery power is required for a give range/run time.
In conventional diver propulsion vehicles, the maximum speed of the vehicle is very close to most users' desirable speed. The motor is not optimized for efficiency at the users' desirable speed. This is means the motor rarely runs at its most efficient point. Low efficiencies mean more power is required for a give range/run time.